In integrated circuit devices adapted to work in one of a plurality of functioning modes, it may be necessary to choose a desired functioning mode at power up of the device. To accomplish this task, integrated circuit devices typically may have one or more mode pins that are sensed at the start-up to read the values therefrom. Depending on the values, the functioning mode of the integrated circuit is chosen. For example, such a pre-established electrical value could be the impedance “seen” on the mode pin: if this impedance is smaller than a certain threshold, it means that a load (for example a smart card) is connected to the pin and the integrated circuit may access to it.
U.S. Patent Application Publication No. 2008/0185444 to Kim et al. discloses an integrated circuit device adapted to function either according to an ISO or to an IEEE functioning mode. A mode detector circuit may be coupled to a plurality of pads to eventually detect a connection to an external load and to choose the functioning mode in which the integrated circuit may work.
In devices that are powered by two supply voltages, such a choice between the two possible functioning modes may be carried out as disclosed in the Japanese Patent Document No. JP 7-30070 without requiring dedicated mode selection pins. According to this approach, the choice of either one or the other operating mode of the integrated circuit is carried out by applying the two supply voltages not simultaneously on the two supply nodes but with a certain time lag. Depending on the succession with which the supply voltages are applied to the two nodes, the integrated circuit device may be started in one or in the other functioning mode. Accordingly, this prior device may always be powered with two external supply voltages, that may both be provided according to a certain time sequence in order to start the device in a desired functioning mode.